Process for producing finely ground sulfur of noncaking character



Jan 1954 R. E. MORNINGSTAR ETAL PROCESS FOR PRODUCING FINELY GROUND SULFUR 0F NONCAKING CHARACTER Filed March 17, 1950 V 2: J m

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O N z 92 3 INVENTORS U- Rolph Eugene Mornipgsfor George H. WhIppIe ATTORNEYS Patented Jan. 12, 1954 UNITED stares PROCESS FOR PRODUCING FINELY. GROUND SULFUR OF NONCAKING. CHARACTER Ralph-Eugene Morningstar, Columbus, Ohio, and George H. Whipple, Wilmington, Del.,' assignors to. Mathieson Chemical .Corporation, a .eorporation of Virginia Application March17, 195,0,SerialNo; 150,128

l6uClaims. :1 Our invention relates to the treatment .of fine- .lygground sulfur and particularly to the-production of finely ground sulfur which issubstantially-non-cakingby heat treatment.

isulfur when in 23,. finely ground form has 11a decided tendencyto cake on storage. The oaking will occur in time with exposure inxan open vesselibut is much more rapid andwsevere-when the; sulfur is subjected to pressure asv inware- .house: storage, whereit may be stacked in'bags .in heights of to feet. The formation of hard lumps in the finely ground sulfur makes it dif- .ficult to blend the sulfur with other agents, as mixed insecticides, and renders application,

for example, dispersion with dusting apparatus, more difiicult.

In order-to overcome this caning tendency of finely: ground sulfur, it.has been the practice to add various conditioning materials to the ground ,sulfur and to dependuponwhatever natural inhibitors may be present. The concentration of conditioners used to prevent caking depends on the nature of the crude sulfur, the conditioning material, and the quality and purity desired in the final product. 'In general the quantity of "the inert conditioner used rangesfrom 2 to 10 PGI'TCBIlt of the-total mixture. Such conditioned .sulfurs, therefore, contain only 90 to 98 per cent .sulfur and obviously are less desirable from'an economic standpoint than pure sulfur. In "addition, the presence of conditioning materials and natural organic inhibitors has the obvious disadvantage that the sulfur product is of limited purity, which must :be taken-into account when athe'sulfuris used. 'Any. deleterious effects of" the conditioner or the contaminatinginhibitors in ,use have to be counteraoted'or may even preclude the use of such sulfur.

We have discoveredthat heat-treatmentof der pressure at ordinary temperatures. The product obtained by our process is free from any added impurities and is not limited in purity-by any dependence on natural contaminants for noncaking qualities. .The process of our invention comprises heating finely ground sulfur to a temperatureifrom about. 95 Cup. to the melting point, maintaining the sulfur at this temperature fora period of time depending upon the tempera ture sufficient to effect the desired conversion,

cooling the mass to a temperature :below about 46C. and reducing. the treated mass to particle form by breaking up the resulting agglomerate to producethe finely ground, nonecaking prodnot. Holding atelevated temperatureapparently effects a change in the physical characteristics-of the sulfur particles so that a non-caking sulfur is produced.

We have further determined that finely-ground sulfur-may be rapidly raised to conversion temperature by heating it in the form of a very thin layer'and that conversion may be completed in bulk storage by the retained heat of the treated mass.

The non-caking sulfur produced by our process is particularly useful as an ingredient in blended mixtures, such as a mixed insecticide, and where application of such mixtures is to be performed by dusting apparatus, the absence of any tendency in the sulfur to cake is a distinct advantage. The product'of our'process is superior in noncaking-characteristics to any conditioned sulfurs we have been able to produce by means of inert conditioner materials, in concentrations up to 1%.

'The finely groundsulfur should be heated to a temperature approaching the melting pointof sulfur in order to produce a satisfactory, prodnot in a reasonable time. The identity of in- :dividual particles must be maintained during the heat treatment; and therefore, any temperature producing'substantial melting is to be avoided. In general, thehigher the temperature used short of melting the sulfur, the more effective is the conditioning operation and the shorter the retention'time necessary. A temperature of 95 .C. or above is usually required to produce the :effect desired inas little as -hour. Tests using 'C.- as a treating temperature failed to yield a sati'sfactoryproduct within a reasonable time. While the sulfur may be maintained at .the treating temperature :in the range of .C. 'up tothe melting point for a considerably longer period than. is required'for the transformation from a-caking to a nomcaking .product, retention time in excess. of a 24-hour period at this temperature may result in sublimation and recrystallization with an undesirable effect on the physical character of theproduct. :Retention times as long as 15 to- 20 hours have shown no harmful. effect on the resultant product.

The heat treated sulfur is characterized by greater homogeneity with respect to particle size, by smoother particle form and by greater particle transparency than the untreated finely divided sulfur. In this-form, the finely divided product is substantially non-caking under ordinary storage conditions. The heat treatment requires sufficient time to effect the desired modificationwhich may be determined by simple test. The higher the temperature, up to thecmelting point, the: shorter the treating time necessary. Forv exampleftreatment at 95 C. usually requires about 80 minutes while-treatment at C. requires on1yabout40-minutes. The-time required varies somewhat with the nature of the crude sulfur and the mode of heating.

A number of means of heating the finely ground sulfur are available, such as conduction from solids and gases and radiation. We have found that the sulfur can be heated rapidly by spreading it in a thin layer on'a heated surface and heating by conduction from the surface. For example, using a test surface of thin metal plate, the temperature-time characteristics necessary to produce a satisfactory product were determined. A boiler was used so that the plate could be heated at different temperatures by'the condensing vapors of liquids of various boiling points, and a layer of finely ground sulfur inch thick covered by a layer of cotton insulation was used. The results of these tests show that the higher the temperature, the shorter the retention time required and the more satisfactory the resultant product. For example, at 95 C. a heating time of 80 minutes was required while at 100 C. and above the retention time was reduced to 40 minutes.

When the finely ground charge is heated to the temperatures of our process, the sulfur agglomerates usually form a firm cake. In order to obtain our non-caking product, it is necessary to break up the agglomerate formed after the heating operation. This can be accomplished effectively by screening. It is first necessary to ,cool the sulfur because the retained heat from the heating operation will cause the sulfur to reagglomerate. We have found that the heattreated sulfur must be cooled below about 46 C. to insure that caking will not occur after the screening operation.

While any suitable means can be used to reduce the agglomerate formed during the heating step once the sulfur is cooled below about 46 0., we have found that the most convenient method is screening. By placing the cooled sulfur on a vibrating screen of appropriate mesh size, the

agglomerate is disintegrated and the sulfur sifted to yield a finished product of desired fineness.

In the following examples illustrative of our invention, we used tests designed to simulate storage conditions to which the final product would be subjected. Twenty gram samples of finely ground sulfur were placed in a brass cylinder l-inch in diameter, capped at one end. A

piston was inserted into the cylinder and comin no caking or in soft cakes that disintegrated easily upon agitation to the finely ground state.

Example] Two samples of Texas Gulf crude sulfur, fog grind, were placed in an oven maintained at a temperature of 105 C. Sample 1 was withdrawn at the end of 1 hour while sample 2 was allowed to remain in the oven for 1'7 hours. Heated samples 1 and 2 were cooled to room temperature and screened to reduce the lumps formed during heating. Samples 1 and 2 plus a sample of the untreated sulfur were stored under pressure. When the samples were removed from storage, the untreated sulfur and sample 1 were caked very hard, but sample 2 showed no caking tendency.

Example II Samples of finely ground sulfur (approximately 325 mesh) were placed in an oven at 105 C. and were withdrawn after different residence times. Samples removed after only 1 or 2 hours showed caking tendencies, and most of these samples caked hard when subjected to the bag test described above. Samples removed after 4 hours or longer (i. e., 7, 12, 16 hours) up to the maximum residence time of 22 hours showed little or no caking tendency and gave a satisfactory to excellent product. All of these samples were cooled to below about 46 C. and screened to disintegrate the agglomerate formed during heating before being subjected to test for caking tendency.

The above method of performing the heating operation does not indicate the minimum time at 105 C. necessary to produce the transformation from caking to non-caking sulfur because it includes the time required to bring the sulfur up to treating temperature. The extra time required by this method is a consequence of the poor heat conductivity of the sulfur and the treatment of the sulfur in bulk. However, where time is available to allow for the slow heating rate, this is a simple method of operation. Usually it is advantageous to treat the sulfur under conditions adapted to optimum heat transfer as illustrated below, but batch heating in an oven gives a satisfactory product and can be employed in a large scale operation.

Example III Samples of finely ground sulfur were spread on the plate heating surface, previously described, in a layer A; of an inch thick and covered with a thick layer of cotton insulation. The underside of the plate was heated by condensing vapors generated by boiling a suitable liquid at a suitable pressure to give the desired plate temperature. By employing this means of heating, it is possible to keep the plate temperature constant. The samples were heated at temperatures of 110 C. and 100 C. for periods of 5, 10, 20, 40 and minutes; then removed, cooled and screened to break up whatever lumps formed during the heating. The samples were tested under compression for caking. The samples heated for 5 and 10 minutes at either 110 C. or C. caked very hard under compression test. The samples heated for 20 minutes at either temperature showed a partial transformation as evidenced by the fact that a firm cake rather than a hard cake was formed when these samples were tested. The samples heated for 40 and 80 minutes at C. or 100 C. gave satisfactory products when tested under compression.

Ezcample IV .The procedure followed and apparatus employed were the same as in the preceding example except that the samples were heated for 40 and 80 minutes at temperatures 110 C. and 895 C. All samples heated for 40 and 80 minutes at temperatures between 110 C. and 975 C. gave satisfactory products when subjected to test. Samples heated in the higher portion of this temperature range and samples heated for longer 'etimesiat. :lower temperatures withinzthis. range? gave superior products- The .sample heated ata959 C. for 80. minutes producedazsoft: cake;- whenitested under compression but was sa-tisface tory'; Samples heated at*92.5 C. andr.S9.5. Co for 80 minutes produced firm cakes 'onzxtest-un-eg der compression;

Inlarge scale operation, it is advantageous to bring the charge quickly up to temperature pun.- I

der:direct"application.of..heat and pass :the hot charge continuously or intermittently to .athot storage systemzwhere conversionis completed under influence of the :retainedheat of "the. sulfur;

charge;

We have. devised a; continuous I system; for

spreading thexfinely divided charge upona heat conducting moving'belt asrathin layer; heating the sulfur layer, discharging the hot sulfur .into aihot .storage .bin or'hopper, withdrawing hot sulfur continuously or. intermittently :fr'omtstor age after sufficient. time, depending-upon; the 1 temperature, to effect conversionrand in lessthan:

about 20m .24 hours, cooling the'tr'eated mass to below about 46 Gland reducing the mass to 1 particle form: Advantageously, the 'layerofsulfur is less than ti -inch in thickness prefera-bly about -inch..

As previously describedythe finelyground sulfur.

should be heated toia temperature approaching theimelting point of sulfur.in :order'to produce a? satisfactory product a reasonable time. Howevelythe identity of. individual particlesmust be .maintained 'duringthe :heat treatment, and

therefore,- any temperature. producing substantial melting is :toloe avoided. Theserequirements 3;)

ofia minimumxretention time in a limited 'ef fctive temperature range together;with the slow": heat transfer rate of finelyg-round sulfur present: the problemof the commercial iapplicationrofthe process.

While the sulfur can be successfully treatedzto:

form a non-caking product in as little as -hour at the conversion temperatures "of. the process; treatment in bulk requires'a'longer period of time to heat the sulfur .to the conversion:temperature than. is requiredforthe actualconversion; For

example, samples .of finely groundsulfurplaced. inian'ioven'maintained at 105C. requir'edrover 2 hours to show signs of conversion to a non caking product and requiredia som'ewhat longer time-etc be effectively converted; However,:. the" finely groundisulfur :can; the rapidly heated. ltotconver sion temperature by spreading the sulfur in athin' layer aonfazheated; heat-conducting surface and heating-the sulfur layerby conduction from 1 theisurface:- A-sulfur layer -inch thick can be: heated to conversion temperature in this wayin'about 1.5 minutes.-

We have found that substantial"advantage-for commercial operation is obtained by using asulfurlayerthickness of-less'th'anabout Af-inch and preferably of approximately /g-incha The advantage of the ab'ove'layer thickness is effec tively'demonstratedby-a-comparison'of the heat ing tir'ne requirecl'fora-"layer flg-inch" thick and the heating time "required for layer thickness of "'l-inch. Under'the same conditions (i. e., thesame thin-metal plate heat-conductingsurface and using a heating medium of condensingsteam at *atmospheric pressure) a sulfur layer *hickness of l-inch'requires' a heatingperiod'in excess of 1'70 minutes to' reach an average tempera ture of 188 'to190 fromzan initial 'room;tem.-

perature; while aflayer'of ISlllflll 2 -inch'inthick 75' c inch.

ness is heated-fronrroom" temperaturato an average temperature of. 88. to 90. .C: m:z;only about inch:

conversionr temperature.-

reduced vtothe 'timeJnecessary to heattthecsulw fur to the conversion'temperature.

ner.

To illustrate the continuous process of our-"ins vention, the following description: is :given with:-

reference to the accompanying drawing; The

drawing is a diagrammatic illustration ofan' apparatus that is suitable to perform ourcona tinuous process of heat treating finely ground sulfur to produce anon-baking product.

sulfur on the conveyor belt *3.

the most favorable heat-transferconditions, but may be formed of other materials. The belt 3 is driven by means of rollers 4 and 4a which are in turn driven bysuitable means (not shown) the spreadingoperation and produces a thin 5 -the heat- 'transferrataof the sulfur does not change, or increases only slightly, when the --sul-' fur is somewhat compressed, the compression roller 6 is placed adjacent to the levelling bar and'compresses the sulfur layer formed b'y'the original height; The'use of the compression ness. In addition, the compressed layers are more easily removed from'the beltsat the dishas a tendency to follow the belt around the discharge roller. Therefore, the feedh'opper I spreads the finely ground sulfur on the'belt, the

70 levelling bar which is constantly agitated to prevent local piling up behindthe bar, spreads the "finely ground'sulfur in a uniform layer ap proximately -inch thick and the compression, roller 6 i compresses this layer to; approximately 1.5 minutess. Thus,;. fora .constant.;heating;sur.-'-;:- facesareazand the :same total heatingrtime' the, amount of sulfur heated .toconversion tempera 5 i tureusing. a sulfur'layer. thicknesszof: 1-inch can; be. .increased by as. much..as.1300% .or moreziby' spreading the sulfur. inra layer thickness Of/.Mgr

In accord-tance with-this embodiment of our-processrthe-z whole operation frominitial heating to reducing:

'the agglomerate after cooling is performed-"m1 a continuous and commercially attractive '-man:-.

Numeral I indicates a-feed hopper-which holds the crude sulfur to betreated. The feedhopper outlet-is shaped in the'formof a spreader" and I" by means of an" agitator'2 spreads thecrude The conveyor b'elt is' formed 'of "thin metal sheet, advantageously stainless steel sheet, in order to obtain to give substantially constant speed. A level-ling bar 5 is positioned abovethe beltto' complete layer of sulfur'of uniform thickness; Because levelli'ng bar to approximately two-thirds the-- roller has the advantage of' increasing the capacity of the apparatus as well'as'allowingthe initial application of'the' finely ground sulfur- 6o layer 'to be-more easily controlled because of the consequent increase in the initial layer thick charge rollers da and Ma. The compressed layer' is'more'cohesiveand tends to break away from the flexing belt while the uncompressed'layer The bottom surface of the continuous conveyor belt 3 is heated for the approximate length of the sulfur travel and the heat is conducted through the belt and into the layer of sulfur. Heat may be supplied in any convenient manner. When a metal belt is used, heating may be effectively accomplished by moving the belt on a bed of hot oil. The rate of heating is controlled to give a trace of melting on the belt in order to insure a maximum discharge temperature of the sulfur. The temperature should be close to the melting point of the sulfur in order to effectively condition the finely ground sulfur in a reasonable time. In general, a temperature of 95 C. will produce a satisfactory product, but by using the heating method described it is possible to obtain a sulfur discharge temperature of approximately 105 C. without melting more than just a trace of the sulfur on the heating belt.

While the sulfur is heated to conditioning temperature on the conveyor belt 3 in a relatively short time, it is necessary that the sulfur remain at this temperature for a longer period of time to complete conversion and, therefore, the storage hopper 8 is provided to hold the heated sulfur for this additional time. The sulfur layer is removed from the conveyor belt at the discharge roller 4a by means of a scraper blade I and falls into storage hopper 8. The sulfur is maintained at the elevated temperature produced by the conveyor belt heating while it remains in the storage hopper. No external heat or insulation is required since the sulfur itself i an eificient insulator. When the process is established under equilibrium flow conditions, the rate at which storage hopper 8 discharges the hot, heat-treated sulfur on the cooling belt is adjusted so that the sulfur is retained in the storage hopper for a period of time sufficient to effect conversion.

After sufficient retention time in storage hopper 8, the sulfur is spread on the cooling conveyor belt 9 in the same manner that is used to charge untreated sulfur to the heating belt. Storage hopper 8 is provided with an agitating device (not shown) to prevent bridging of the hot caked sulfur. The cooling conveyor belt 9 is driven by means of rollers l and [0a which, in turn, are driven by suitable means (not shown) to give a substantially constant speed. The levelling bar H and compression roller l2 level and compress the finely ground sulfur on the cooling belt 9 to a final layer thickness of approximately /;-inch. A suitable cooling means is employed to withdraw heat from the bottom of the cooling belt in order to cool the sulfur below about 46 C. When a-metal belt is used, the cooling means may be provided by moving the belt on a bed of coolant, advantageously water.

,The finely ground sulfur cooled to 46 C. or below is removed from the cooling belt 9 by means of a scraper blade l3 positioned to work against the belt at the discharge roller 10a. The agglomerate formed during the heating operation is discharged from the belt to the inclined vibrating screen I 4. The vibrating screen, formed of screening of appropriate mesh size, acts to break up the agglomerate and sift the finished product so that it is discharged from the apparatus as a final product at l5. Agglomerate that is not broken up by the action of the vibrating screen by the time it gravitates t0 the bottom of said screen is transferred to an elevator Hi. The elevator l3 lifts the material rejected by the screen to a point above the top of the inclined screen, transfers the material to a screw conveyor 11 which returns the rejected material to the top of the inclined vibrating screen M for further classification.

As a further example of the operation of this continuous embodiment of our process, including specific operational conditions for the heating cycle of the process, the following test run is described.

A two-ply canvas belt, dyed black to promote heat transfer, was used for the heating surface.-

The feed hopper, driving rollers, levelling bar and compression roller were essentially the same as in the previously described apparatus. Heat was supplied by means of infra-red lamps. The lamps were controlled by transformers to regulate the heat supplied to the belt to obtain as high a discharge temperature as possible with just a trace of melting on the belt. Some of the lamps were used to preheat the belt.

The belt was 24 inches wide and 15 feet total length. The distance from the levelling bar 5 at the feed end of the belt to the point of discharge into the storage hopper was 4 feet 10 inches. The thickness of the feed was -inch at the levelling bar compressed to /;;-inch by the compression roller. The rate of feed was pounds per hour. The driving rollers were driven at such a speed that exactly 2 minutes were required for the belt to travel from the leveling bar to the discharge roller. This time, 2 minutes, was dictated by the heat-transfer rate. A layer of sulfur A;-inch thick requires approximately 1 /2 to 2 minutes to reach conditioning temperature. Production rates of feed and, therefore, output would be accomplished by means of longer belts moving at higher velocities. Output may be additionally increased of course by an increase in belt width.

After the finely ground sulfur was heated on the belt, it was discharged into the storage hopper. The storage hopper temperature was 99 C. and the sulfur was maintained at this temperature about one hour. The sulfur was then cooled and screened. The resultant product was tested and proved satisfactory on storage under pressure.

When using our continuous process, the belt length and the belt velocity for the heating cycle are determined by the desired production rate,

the width of the heating belt and the sulfur layer thickness. The thickness of the sulfur layer used in the process determines the heating time required and, therefore, the necessary residence time on the heating belt. Assuming a production rate of 5,000 pounds per hour, a heating belt width of 2 feet and a sulfur bulk density of 38 pounds per cubic foot, the required belt velocity and belt length can be determined for any particular sulfur layer thickness. As noted above, the

time necessary to heat a sulfur layer l-inch thick is greater than minutes as compared to 1.5 minutes required for a layer only %-inch thick. Under the same conditions a sulfur layer A-inch thick requires approximately 7 minutes. Therefore, under the assumed conditions a belt greater than 2,240 feet in length traveling at about 13 feet per minute would be required for a sulfur layer l-inch thick. A belt approximately 370 feet in length and a belt velocity of approximately 53 feet per minute would be necessary with the -inch layer.

By using a sulfur layer V -inch in thickness the belt length is reduced to ap-- proximately 158 feet and the belt velocity increases to about 106 feet per minute. This comparison of required belt length and belt velocity is a further illustration of the commercial advantage of the use of sulfur layers less than about fl -inch in thickness and advantageously approximately -inch in thickness. While shorter belts could be used with layer thicknesses less than /8-inch, the rapid increase in required belt velocity and the problem of spreading such thin layers onthe belt make the use of layer thicknesses less than about 4 -inch commercially unattractive.

For commercial operation it appears that the effective heating surface area should be about 100 square feet per hourly ton of sulfur treated. Because of the higher temperature differential encountered in the cooling operation, the efiective cooling area need not be as large to accommodate the same amount of product. Based on the use of water at a temperature of approximately 80 F. as the coolant, an effective cooling area of about 40 square feet per hourly ton of sulfur should be adequate.

Our heat-treated sulfur is characterized by greater homogeneity with respect to particle size, by smoother particle form and by greater particle transparency than the untreated finely ground sulfur. Under the microscope, samples of the treated material show particles of smoother, less jagged edges in contrast to untreated sulfur of similar source. Maximum particle size appears unaffected, but there is an appreciable reduction in the presence of fines. Photomicrographs show greater transparency for the treated particles. In this form the finely divided product is substantially non-caking under ordinary storage conditions.

Because of these observable differences between the character of treated and untreated sulfur and in view of the fact that sulfur is a volatile solid, it is believed that the heat treating mechanism may involve a mass transfer. Caking then may be associated with irregular jagged particle edges. Under the influence of heat above say 46 C. and up to the melting point, a vapor pressure disproportionation is set up as a result of the varying surface configuration so that the irregularities tend to become smoothed out at a rate governed by the temperature by mass transfer caused by vapor pressure differences rather than temperature differences in the mass.

Our invention of course does not depend upon this hypothesis but provides regardless of the correct mechanism a finely divided sulfur product of non-caking character and heat treating means for producing it.

This application is a continuation-in-part of our copending application Serial No. 142,097 (now abandoned).

We claim:

1. A process for producing finely ground sulfur of non-caking character which comprises spreading finely ground sulfur on a heat-conducting surface in the form of a thin layer, heating the sulfur layer to a temperature in the range of about 95 C. up to the melting point of the sulfur, discharging the heated sulfur into a hot storage zone, withdrawing the sulfur from said storage zone after sufficient time to effect such conversion and in less than about 24 hours, cooling the sulfur below about 46 C. and reducing the treated mass to particle form.

2. A process for producing finely ground sulfur of non-caning character which comprises spreading finelyground sulfur on a heat-conducting surface in the form of a thin layer of about A;-inch thickness, heating the sulfur layer to a temperature in the range of about C. up to the melting point of the sulfur, discharging the heated sulfur into a hot storage zone, withdrawing the sulfur from said storage zone after suificient time to effect such conversion and in less than about 24 hours, cooling the sulfur below about 46 C. and reducing the treated mass to particle form.

3. A process for producing finely ground sulfur of non-caking character which comprises spreading finely ground sulfur on a heat-conducting surface in the form of a thin layer of about inch thickness, heating the sulfur layer to a temperature of approximately 0., discharging the heated sulfur into a storage hopper wherein the sulfur is maintained at said temperature, withdrawing the sulfur from said storage zone after about 40 minutes and in less than about 15 hours, cooling the sulfur below about 46 C. and reducing the treated mass to particle form.

4. A process for producing finely ground sulfur of non-caking character which comprises spreading finely ground sulfur on a heat-conducting continuous belt in the form of a thin layer, compressing said layer to a thickness of about A;- inch, heating the sulfur layer to a temperature in the range of about 95 C. up to the melting point of the sulfur, discharging the heated sulfur into a hot storage zone, withdrawing the sulfur from said storage zone after sumcient time to effect such conversion and in less than about 24 hours, spreading the hot sulfur on a second heat-conducting continuous belt in the form of a thin layer, compressing said layer to a thickness of about -inch, cooling this sulfur layer below about 46 C., discharging the cooled sulfur onto a vibrating screen and reducing the treated mass to particle form.

5. A process for producing finely ground sulfur of non-caking character which comprises heating finely ground sulfur to a temperature in the range of about 95 C. up to the melting point of the sulfur, maintaining the sulfur in solid form in said temperature range for a period of time from about one-half hour to not more than about 24 hours and sufiicient to efiect such conversion, cooling to a temperature below about 46 C. and reducing the mass to particle form.

6. A process for producing finely ground sulfur of non-caking character which comprises heating finely ground sulfur to a temperature of approximately 105 C., maintaining the sulfur in solid form at this temperature for at least about 40 minutes and not more than about 15 hours, coollng the sulfur to a temperature below about 46 C. and reducing the mass to particle form.

RALPH EUGENE MORNINGSTAR. GEORGE H. WHIPPLE.

Mellor: "A Comprehensive Treatise Theoretical Chemistry, vol. 10, pages 24, 25. London, Longmans, Green and Co. (1930) Number 

1. A PROCESS FOR PRODUCING FINELY GROUND SULFUR OF NON-CAKING CHARACTER WHICH COMPRISES SPREADING FINELY GROUND SULFUR ON A HEAT-CONDUCTING SURFACE IN THE FORM OF A THIN LAYER, HEATING THE SULFUR LAYER TO A TEMPERATURE IN THE RANGE OF ABOUT 95* C. UP TO THE MELTING POINT OF THE SULFUR, DISCHARGING THE HEATED SULFUR INTO A HOT 